Yeast

The name of this species of yeast, Saccharomyces cerevisiae, is quite a mouthful, but maybe that's appropriate. This and other similar yeasts are used to make a lot of the food and drink we enjoy during the winter holidays. Bread, beer, wine, and spirits are all made possible by a chemical process called fermentation which these tiny, one-celled fungi carry out. The ones we use are often called "budding yeasts" because they reproduce asexually— tiny buds form on a yeast and break off as they grow, creating a more or less identical copy of the "parent". Because of what we use them for, you'll see them called "baker's yeast", "wine yeast", or "brewer's yeast" as well.

Fermentation happens when yeasts break down sugar; something they love to do, since it's how they get their energy. As they eat the sugars, they produce two waste products: alcohol and carbon dioxide. Humans have been taking advantage of this for thousands of years; as long ago as we can remember, really. When we bake bread, the alcohol burns off, but the carbon dioxide makes bubbles which fluff it up nicely, and by giving a bunch of sugar from grapes or hops to some yeast and letting them feed off it in a controlled way, we make alcoholic drinks like wine and beer. The carbon dioxide bubbles come in handy to make the fizz in beer and champagne, too.